Nurr1, an orphan receptor of the nuclear receptor superfamily, is widely expressed in the central nervous system (CNS) including brain regions where dopaminergic neurons are abundant. Recent analyses of Nurr1 null mutant mice, have shown that Nurr1 is essential for the development and survival of midbrain dopaminergic neurons. However, other dopaminergic neuronal populations do not seem to be affected by ablation of the Nurr1 gene. To better characterize the selective effects of Nurr1 on catecholaminergic neurons, we have used anatomical techniques to examine the degree of co-existence of Nurr1 mRNA and tyrosine hydroxylase (TH) immunoreactivity in the brain of adult mice. Our results indicate that the majority of TH immunoreactive neurons in the substantia nigra compacta (SN; 96%), ventral tegmental area (VTA; 95%), retrorubral field (91%), olfactory bulb (85%), linear nucleus raphe (91%), and central grey (61%) express Nurr1. In contrast, dopaminergic cells of the paraventricular and periventricular hypothalamic nucleus showed only a few Nurr1/TH double labeled neurons, whereas TH immunoreactive neurons in the arcuate nucleus and zona incerta did not express Nurr1 mRNA. Nurr1 expression was also excluded from (nor)adrenergic neurons of the brain stem. In conclusion, Nurr1 transcripts were not found in all CNS catecholaminergic neurons. Nurr1 expression was confined to periglomerular and midbrain dopaminergic neurons. These results suggest that within the adult mouse brain, Nurr1 may participate in dopaminergic functions of the olfactory bulb and midbrain. The high levels of Nurr1 expression within the midbrain dopaminergic neurons indicate the possible role of this transcription factor in regulating genes that are likely to influence the functions of nigrostriatal and mesolimbic dopaminergic pathways. - Dopamine, Substantia Nigra, Development